Solar collectors are used in many applications to collect solar energy and to convert it to heat. In recent years, such collectors have enjoyed increasing popularity, because, once installed, they provide a relatively cost-free source of hot water for domestic usage and for home heating. Generally, a collector consists of a glass-covered array of fluid-filled tubes carried on a flat plate. The plates are designed to optimize the absorption of radiant sunlight and thus the conversion of the energy into thermal energy in the fluid passing through the tubes. The fluid in the tubes is circulated through a thermal capacitor where a heat exchange occurs. Heat, usually in the form of hot water, subsequently may be drawn from the capacitor, to provide for domestic needs or to supplement traditional heating systems.
Development of solar-heating systems in the northern portions of this country, however, has been hampered by the problem of heat loss to the ambient air in the collector and eventually to the outside air. The solutions to this problem to date have been less than satisfactory. Caulking of the frame may be employed, but the ambient air in the collector still will carry heat from the collector plate to the glass cover where it will dissipate to the outside. A plurality of glass plates also may be employed to retard heat loss; however, the more cover plates, the greater fraction of sunlight is absorbed or reflected by them and the lesser percentage of solar energy is available to the collector plate. Thus, it would be most desirable for a solar collector to be formed in a manner, whereby heat loss would be minimized, yet, at the same time, maintaining a single-sheet, glass-cover construction.